Method of Estimating Pulse Response Using an Impedance Spectrum

Abstract

Electrochemical Impedance Spectrum (EIS) data are used directly to predict the pulse performance of an energy storage device. The impedance spectrum of the EIS is obtained in-situ using pre-existing techniques. A simulation waveform is configured such that the period of the pulse is greater than or equal to the lowest frequency of the impedance measurement. If the pulse is assumed to be periodic for analysis purposes, the complex Fourier series coefficients can be obtained. The number of harmonic constituents are selected so as to appropriately resolve the response, but the maximum frequency should be less than or equal to the highest frequency of the impedance measurement. In some cases, the measured frequencies of the impedance spectrum do not match the corresponding harmonic components of the simulated pulse wave. This is resolved by estimating the impedance measurements at the desired frequencies using linear interpolation, cubic spline fits, or other comparable methods. Using a current pulse as an example, the Fourier coefficients of the pulse are multiplied by the impedance spectrum at the corresponding frequency to obtain the Fourier coefficients of the voltage response to the desired pulse. The Fourier coefficients of the response are then summed reassemble to obtain the overall time domain estimate of the voltage using the Fourier series analysis. Thus, the response of an energy storage device to an anticipated or desired pulse can be estimated using low-level, charge neutral impedance measurements combined with Fourier series analysis.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefits of U.S. Provisional Patent Application No. 61 / 186,358; filed Jun. 11, 2009. The disclosure of this application is hereby incorporated by reference in its entirety, including all figures, tables and drawings.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]This invention was made with government support under Grant No. DE-AC07-05ID14517 awarded by the United States Department of Energy. The government has certain rights in the invention.REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX[0003]Not Applicable.BACKGROUND OF THE INVENTION[0004]Energy storage devices (e.g., batteries, fuel cells, ultracapacitors, etc.) have become significantly more prevalent in many government and commercial applications (e.g., automotive, military, space, electric utilities, medical, etc.). Consequently, there has also been an increased interest in smart monitorin...

AI Technical Summary

Benefits of technology

[0013]Thus, the ESD response of a pulse excitation can be estimated based on a simple impedance measurement combined with the Fourier coefficients of a simulated pulse. The estimated response behavior can be used by smart monitoring systems to more effectively manage ESD usage. For example, if the estimated response exceeds a desired threshold, the smart monitoring system can either shutdown operations, or iteratively determine a pulse excitation level than can be successfully applied to the ESD without violating operational limits (e.g., managing how much power assist is provided by the ESD in automotive applications). A smart system can also use this information to know when warning signals should be sent to a user prior to a demand being placed on the ESD.

Problems solved by technology

In some cases (e.g., with Fast Summation Transformation), the impedance spectra will be lower resolution than desired due to the need for a very rapid measurement.

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